Artificial insemination (AI) and embryo transfer are widely used techniques for delivering biological liquids containing semen or embryos into the reproductive tract of a female animal. Such techniques are routinely used in livestock breeding and introducing new genetic lines into an animal herd, especially dairy cattle and swine (pigs).
Artificial insemination techniques for livestock typically utilize liquid extended semen. In practice, fresh semen collected from a boar is combined with a semen extender, an aqueous solution used to dilute the ejaculate to obtain a large number of doses that can be used for inseminating multiple sows, e.g., up to 200 sows.
The extender functions to provide membrane stabilization in cool storage temperatures, an energy source for sperm metabolism, pH buffering, ions for membrane and cell balance, and antibiotics to prevent microbial growth. The proper extension of semen is critical to the success of the insemination procedure, and it is vital that extended semen doses possess acceptable characteristics to be capable of impregnating a gilt or sow which is inseminated at the appropriate time. In the U.S., artificial insemination protocols for swine recommend carrying out inseminations with a dose of 70 to 90 ml (cc) containing 3 to 3.5 billion spermatozoa per dose. European protocols typically use about 1.5 billion sperm per dose.
Extending the semen needs to be done while preserving the functional characteristics of the sperm cells (spermatozoa). Seminal plasma within the ejaculate supplies the sperm cells with nutrients for a limited period. To preserve the sperm cells for an extended period, their metabolic activity is reduced by diluting the cells in an appropriate liquid extender medium and lowering the temperature. To perform its function, the extender should supply the nutrients needed for the metabolic maintenance of the sperm cell (glucose), afford protection against cold shock (BSA), control the pH (bicarbonate, TRIS, HEPES) and osmotic pressure (NaCl, KCl) of the medium, and inhibit microbial growth (antibiotics).
In current semen extension processing, the fresh semen is diluted with a semen extender to the desired dosage concentration and the dose amount (e.g., 80 cc) is dispensed into and sealed within a semen container as a ready-to-use semen dose. In a livestock insemination procedure, the container holding the semen is attached to a semi-rigid tube or catheter which has been inserted into the female animal (sow/gilt) to be inseminated. Muscular contractions then aid in drawing the seminal fluid into the body of the sow or gilt.
Excessive or abrupt dilution of semen or the exposure of spermatozoa to a solution with a relatively high concentration of solutes (hypertonic solution) can lead to what is known as a ‘dilution effect’ or osmotic shock and a permanent loss of motility, metabolic activity and fertilizing capacity. Generally, when sperm cells are exposed to a hypertonic solution (e.g., an extender solution), water is initially drawn out of the cells into the surrounding medium resulting in dehydration and shrinkage of the cells, followed by an influx of water causing the cells to swell to balance the internal and external osmotic pressures. If the semen extender is abruptly added (or the semen is excessively diluted), cell shrinkage and swelling can occur rapidly and excessively resulting in physical damage to the cells with a loss of sperm motility and function. For this reason, the semen should be diluted slowly or by step-wise addition of the extender to allow for a gradual osmotic adjustment between intra- and extracellular fluids to minimize osmotic shock. However, this is both tedious and time consuming.
Other problems in extending the semen concern the protracted exposure of the sperm cells to certain solutes, which can be detrimental causing toxic injuries to the cells. In addition, the amount and composition of semen extender and number of sperm cells for currently practiced insemination dose amounts gives rise to high production costs and an economic impact on a breeding operation.
Containers for holding semen are known. For example, U.S. Pat. No. 8,025,855 (Kuhlow) discloses a semen container having a hollow body with an open, sealable end and a nozzle at the opposing end fitted with a removable tip. In another example, U.S. Pat. No. 6,551,819 (Simmet) discloses a container for semen and other biological liquids that includes a nozzle for delivery of the liquid with means for bending of the nozzle such that the container can be positioned in a vertical alignment while attached to a horizontally aligned catheter without kinking of the container or catheter which can hinder delivery of the biological liquid from the container to the animal. The vertical positioning of the container facilitates gravity flow, which assists the transfer of the biological liquid from the container into the catheter and the sow/gilt being bred.
Known sperm containers are structured to contain an insemination dose of 80 to 100 ml containing 3 to 3.5 billion sperm cells, which requires careful processing to avoid osmotic shock during the dilution process. In addition, with current containers, sperm cells are continuously exposed to the solutes of the extender solution without the ability to modify the solution during the storage period.
It would be desirable to provide a container for an insemination dose that overcomes the foregoing problems.